At 07:51 PM 04/19/07, you wrote: >I have a remote base setup on a UHF machine running an RC-210. I would >like to be able to remotely rotate a beam antenna via DTMF over the >repeater. I have figured a way to do this via the controller, but I have >not yet figured out how to know where the beam in pointed. I have seen >several brands of electronic compass senors, but not sure if there was a >way to incorporate one of these devices to determine beam direction. >After looking around, I am starting to think I may have to do something >along the lines of using a PC in some sort of configuration to >accomplish this. Just not sure how to get the ball going in the right >direction. Has anyone else done a project like this? Care to share any >ideas? > >Thanks >Steaven, W4YI
20-25 years ago the Cactus Radio group in southern california had a similar problem. They had a 2m remote base on a mountain top and needed to control a beam. They came up with the Cactus Radio Antenna Pointer Circuit. The abbreviation is obvious. This was a multi-card all-TTL solution that interfaced to the existing control system, which (aside from the crosspoint audio switching) was itself all TTL logic. One part of the circuit read the variable resistor in the rotator, converted it into a digital value, and stored it in a register. On a touchtone command it converted it to morse (using a PROM based lookup table) and sent the bearing back to the requester in MCW. Another part of the circuit accepted a bearing in touchtone, compared it to the current value, decided if it was less than or greater than or equal to and twisted the beam the proper direction. If it was equal it sent a function complete message (i.e. beep-beep) and the bearing in MCW. If it was not equal it sent the function complete and started the rotator turning the proper direction. Once the bearings matched the rotator was stopped, the brake was engaged and the current bearing (i.e. the new bearing) was sent. If the bearing didn't change in the first few seconds after power was applied to the rotator, and continue to change as it rotated the process aborted and sent back "FR" in morse (for "frozen"). Not frozen mechanically, but as in something interfering with rotation, perhaps ice on the antenna and rotator. Icing was minimized by cutting a hole in the bottom of a common one-gallon plastic bucket with a saw, then cutting it from the center to the outside then fitting it upside down over the rotator. BTW all of this was implemented somewhere in the late 70s to mid 80s, if I remember correctly, and I heard about it over dinner several years after it was put into operation. The 2m station, as it was described to me, was a 250w Motrac base station with 12 channels and several PL encode tones. There were two antennas, the beam and a Stationmaster, selected by an antenna relay that was housed in a rural mailbox. So yes, a remotely controlled beam has been done, but it could be done much easier these days in a modern repeater controller. I've seen a RS-232 controlled rotator box, so that much is already done. A cable to a serial port on the controller is trivial. If the price on a serial controlled rotator control box exceeds the budget, then connecting three digital outputs to a pair of directional relays and a brake relay all wired into a rotator control box, and reading the DC analog voltage coming back from the rotator potentiometer would be not particularly difficult, just time consuming. The analog to digital conversion is a few lines of code in a PIC chip, and it and all the relays could be mounted inside the rotator box and connected via a DB9 mounted to the rotator box cabinet wall. The rest is all controller firmware - a meter face of 0 to 359 degrees plus some code. And the code has to include a "coasting" fudge factor... i.e. how far the antenna continues to rotate after the motor power is removed, and once completely stopped the brake can be re-engaged. Mike WA6ILQ
